<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>利用边框实现CSS绘图</title>
    <style>
        .k{
            width: 0;
            height: 0;
            border: 100px solid transparent;
            /* border-color: red green blue orange; */
            border-color: red transparent;
            transition:  all .5s;
        }
        .k:hover{
            border-color: red transparent blue transparent;
        }
    </style>
</head>
<body>
    <div class="k"></div>
</body>
</html>